The present invention relates generally to the formation of spray nozzles along a fluid conduit, and more particularly, to a wash arm for a dishwashing machine and a method and apparatus for forming the same.
Virtually all dishwashers, whether commercial or domestic, operate by directing pressurized streams of heated washing liquid consisting of water and detergent against the ware to be washed. The heated water sanitizes the ware, while the pressurized streams strip soil particles from the ware. These streams typically emanate from a plurality of nozzles which are formed along one or more fluid conduits or wash arms. A pumping system directs water into the wash arm, and the water then exits through the nozzles for cleansing of the ware. In order to properly clean the ware, complete coverage is required.
A number of different nozzle constructions have been used in dishwashing machines, along with a range of methods for forming the nozzles. In general, such variety has been caused by the variety in types of dishwashing machines, in which different needs in terms of nozzle performance are typically present.
Several examples of wash arm and nozzle construction can be seen in U.S. Pat. No. 4,439,242 issued Mar. 27, 1984 to Hadden. One type of wash arm is shown for use in a commercial dishwasher designed to wash only a single rack of ware at any one time. Upper and lower wash arm assemblies are provided, each comprising a pair of fluid conduits extending in opposite directions from a central hub. Each conduit has several bosses formed along its length, directed generally toward the interior of the wash chamber. A slot is formed on each boss to extend in a direction parallel to the conduit. The bosses are formed to direct water from the slots in a somewhat rearward direction with respect to the desired direction of rotation of the arm about the central hub. Thus, the water pressure as the water emerges from each slot also causes rotation of the arms.
Most dishwashers recycle wash water, and it is therefore quite difficult if not impossible to prevent some soil or debris washed from the ware from being recirculated through the wash arms. Although the water is typically filtered, the filters are generally fairly coarse to avoid restriction of water flow. Because the bosses of the nozzle construction just described extend outwardly from the fluid flow path along the conduit interior, such debris tends to move into the bosses and remain there, since the debris is then sheltered from the primary flow path. To make certain that such debris does not clog the nozzle openings, the slots are made relatively large so that the debris can easily pass through each slot.
By forming large slots, the fan-shaped water stream emerging from each nozzle cannot be strictly defined. This is not a critical limitation, since the rotation of the wash arms insures adequate water coverage of the ware. However, the large quantity of water that must be pumped through such slots requires a high capacity, and hence more expensive, pumping system.
The Hadden patent also discloses a conveyor-type commercial dishwasher in a which a different wash arm construction is used. In such a machine, a plurality of arms are disposed above and below the conveyor path, extending generally laterally across each rack of dishes as it is moved through the machine. Because the arms are stationary, more precise direction of the water streams emerging from each nozzle is required to achieve adequate coverage. Accordingly, a fan-like structure is attached to the exterior surface of each conduit, with a slot formed through the conduit and opening into the interior of the structure.
Since the fan-like structures are used to direct the water streams instead of bosses, clogging of slots by debris is reduced, and slot size can be smaller. A lower-capacity pumping system can then be used. However, while this type of wash arm and nozzle construction provides for well-defined and accurately directed water streams, it represents a relatively expensive means of wash arm construction. The fan structures must be fabricated and then individually attached along each wash arm.
Another method for forming a wash arm, used in a domestic-type machine, is disclosed in U.S. Pat. No. 3,323,529 issued June 6, 1967 to Geiger et al. Each wash arm is formed from trough-like upper and lower half portions, which are subsequently attached by crimping along the side edges of the half portions to form the entire arm. Formed within one half portion of the arm are a series of spherical inward impressions, each having a slot defined therein through the portion. The impressions and slots define the nozzles along the wash arm, and are formed at the same time as the half portion is initially fabicated by stamping the halves from sheet material.
The inward impressions formed in the wash arms substantially solve the problem associated with outward bosses, in that soil particles do not collect around the nozzle area. However, the stamping procedure requires a significant investment in tooling, as does the machinery for crimping the halves to form the completed wash arm. This increases the cost of manufacturing for each dishwasher, and is a particularly significant problem for large commercial type dishwashing machines, such as those shown in the Hadden patent. Since relatively small numbers of such machines are manufactured, the relatively expensive tooling to form such wash arms repesents an economic drawback.
What is needed, therefore, is a relatively simple method for forming a fluid conduit having spray nozzles for use as a dishwasher wash arm. The method must be able to produce wash arms at relatively low cost and with a relatively small investment in tooling. A wash arm formed by such a method should tend to resist clogging of nozzle openings by soil particles, and should be capable of producing relatively well-defined and accurately positioned water streams. This will enable such an arm to be used in a variety of types of machines.